While I wait for the first set of abusive angry comments and helpful emails about bugs to arrive, I've decided to investigate 2G/3G toggling. I've put this off for the moment, because my phone network only supports 3G. However, in a months time I'll be switching to another network, so I'll appreciate whatever battery savings a 2G/3G toggle will provide.

I've thrown together a simple test app and am pleased to say it works great on my phone... a HTC Desire Z running CyanogenMod 7. However, I'm fairly sure the CM guys have tweaked their version of Android to allow the network mode to be changed without any special permissions being required.

I'd be interested to hear whether it works for you! If you decide to try it, let me know your phone and ROM.